tokio-xmpp client: condense fn connect(), refactor out into stream_features

tokio-xmpp/src/stream_features.rs

@@ -0,0 +1,45 @@
+//! Contains wrapper for `<stream:features/>`
+
+use xmpp_parsers::Element;
+use crate::starttls::NS_XMPP_TLS;
+use crate::client::{NS_XMPP_SASL, NS_XMPP_BIND};
+use crate::error::AuthError;
+
+/// Wraps `<stream:features/>`, usually the very first nonza of an
+/// XMPPStream.
+///
+/// TODO: should this rather go into xmpp-parsers, kept in a decoded
+/// struct?
+pub struct StreamFeatures(pub Element);
+
+impl StreamFeatures {
+    /// Wrap the nonza
+    pub fn new(element: Element) -> Self {
+        StreamFeatures(element)
+    }
+
+    /// Can initiate TLS session with this server?
+    pub fn can_starttls(&self) -> bool {
+        self.0
+            .get_child("starttls", NS_XMPP_TLS)
+            .is_some()
+    }
+
+    /// Iterate over SASL mechanisms
+    pub fn sasl_mechanisms<'a>(&'a self) -> Result<impl Iterator<Item=String> + 'a, AuthError> {
+        Ok(self.0
+           .get_child("mechanisms", NS_XMPP_SASL)
+           .ok_or(AuthError::NoMechanism)?
+           .children()
+           .filter(|child| child.is("mechanism", NS_XMPP_SASL))
+           .map(|mech_el| mech_el.text())
+        )
+    }
+
+    /// Does server support user resource binding?
+    pub fn can_bind(&self) -> bool {
+        self.0
+            .get_child("bind", NS_XMPP_BIND)
+            .is_some()
+    }
+}